Tensiometer assembly for substitution type analytical balances

ABSTRACT

A tensiometer assembly for use with substitution type analytical balances that is particularly designed to take the place of the conventional weighing pan with which such balances are commonly provided. The tensiometer assembly comprises an elongated support mechanism having a support eye at the upper extremity thereof that is adapted to be received by the hook portion of the weighing arm of a substitution type analytical balance, thereby suspending the tensiometer assembly in vertical relation within the weighing chamber of the balance. The support mechanism includes a needle chuck device, disposed at the lower extremity thereof, that is adapted to support a conventional duNouy ring in substantially rigid relation with the support mechanism. A container for a liquid defining the interface to be tested may be raised or lowered in accurately controllable manner by a movable support device. The support device may be capable of moving the container downwardly at a controlled rate of speed thereby moving the interface downwardly past the ring portion of a duNuoy ring or other suitable tensiometer device suspended in the liquid by the support mechanism. The force necessary to move the duNuoy ring through the liquid interface is accurately measured by the analytical balance.

United States Patent [191 Graham TENSIOMETER ASSEMBLY FOR SUBSTITUTIONTYPE ANALYTICAL BALANCES OTHER PUBLICATIONS Janz, G. J. et al., PreciseMeasurement of Density & Surface Tension, ln Rev. of Sci. lns., 3l(l)-p.18-22, Jan. 1960.

Primary Examiner-Richard C. Queisser Assistant Examiner-Joseph W. RoskosAtt0rneyTom Arnold et al.

[ Dec. 25, 1973 [5 7] ABSTRACT A tensiometer assembly for use withsubstitution type analytical balances that is particularly designed totake the place of the conventional weighing pan with which such balancesare commonly provided. The tensiometer assembly comprises an elongatedsupport mechav nism having a support eye at the upper extremity thereofthat is adapted to be received by the hook portion of the weighing armof a substitution type analytical balance, thereby suspending thetensiometer assembly in vertical relation within the weighing chamber ofthe balance. The support mechanism includes a needle chuck device,disposed at the lower extremity thereof, that is adapted to support aconventional duNouy ring in substantially rigid relation with thesupport mechanism. A container for a liquid defining the interface to betested may be raised or lowered in accurately controllable. manner by amovable support device. The support device may be capable of moving thecontainer downwardly at a controlled rate of speed thereby moving theinterface downwardly past the ring portion of a duNuoy ring or othersuitable tensiometer device suspended in the liquid by the supportmechanism. The force necessary to move the duNuoy ring through theliquid interface is accurately measured by the analytical balance.

11 Claims, 6 Drawing Figures PATENTEU nEc 2 5 1915 SHEET 10F 2 PATENTEDM1225 I975 SHEET 2 SF 2 TENSIOMETER ASSEMBLY FOR SUBSTITUTION TYPEANALYTICAL BALANCES FIELD OF THE INVENTION The present invention relatesgenerally to the measurement of surface tension and the measurement ofthe speed at which surface molecules spread. More particularly, theinvention relates to the combination, with a substitution typeanalytical balance, of a mechanism providing the substitution balancewith the capability for measuring surface tension and for measuring thespreading speed of surface active molecules through employment of theconventional duNouy principle of surface tension measurement.

The ability to measure surface and interfacial ten- 15' BACKGROUND OFTHE INVENTION Measuring of surface tension and measurement of thespreading speed of surface active molecules of a liquid are generallyaccomplished by specialized measuring instruments that are specificallydesigned with single measurement capability. Virtually no universalmeasuring and weighing instruments are available that have thecapability of conventional weighing and the measurement of the surfacetension properties of a liquid in addition to the capability formeasuring the spreading velocity of surface-active molecules. It istherefore generally necessary to provide specialized testing equipmentat considerable expense in the event both weighing and surface tensionmeasurement are to be conducted at a single laboratory facility.

Where surface tension. measurements are to be conducted, it is seldompossible to obtain accuracy greater than plus or minus 0.1 dynes per cm.unless the tensiometer provided is delicately constructed with a highdegree of mechanical and electrical sophistication to obtain anunusually high degree of accuracy. It is virtually impossible, however,to obtain surface tension measurements with the accuracy of asubstitution type analytical balance although in many cases such isdesirable.

Generally, a laboratory that would require a facility for measuring thesurface tension of a liquid or the interfacial tension between liquidsis also provided with an analytical balance to accomplish accurateweighing. Many such laboratories in fact are provided with analyticalbalances that employ the principle of substitution weighing to achieveprecise measurement beyond the capability of most two pan typeanalytical balances. Accurate weighing under ideal circumstancesrequires that the weight of an unknown object be compared with a knownweight under exactly the same conditions. The principle of substitutionweighing has been found to provide weighing accuracy that is superior tomost other weighing instruments. It would be desirable,

therefore, to utilize the weighing accuracy of substitution typeanalytical balances to measure the surface tension of liquids to thedegree of accuracy ordinarily within the capability of such instruments.

THE PRIOR ART Devices for measuring surface tension by the duNouyprinciple have been in use for quite some time as evidenced by the U. S.Pats. to Schoenburg No. 1,960,224, Dopel No. 2,756,587 and Heneage No.3,043,131. The duNouy principle of surface tension measurement has beenincorporated into any number of different measuring devices that mayemploy mechanically induced variations of electrical current to producegreater measuring sensitivity than is ordinarily practical withmechanical measuring or weighing mechanisms. Certain of the surfacetension measuring instruments may measure the concentration of surfaceactive substances by employment of an adhesion element that is suspendedfrom a balanced mechanism constructed specifically for this particularpurpose (Hettche et al, U.S. Pat. No. 2,895,329). Measuring andrecording of the boundary surface properties of various liquids has alsobeen accomplished through the use of a Wheatstone bridge measuringcircuit that measures the degree of torsion of a horizontally disposedtorsion wire that is energized directly responsive to forces created bysurface tension (Sucker et al, US. Pat. No. 3,415,109). Surface tensionhas also been measured by strain-gauge type testing machines employing aload cell, (Review of Scientific Instruments, Vol. 29, No. 9, Sept.1958, pp 785-787).

Where interfacial tension between murky or opaque liquids, such as crudeoil and water containing a fine dispersion of particles, is to bemeasured, it becomes relatively impossible to employ conventionalmethods such as the drop volume method or the pendant drop method ofmeasuring the interfacial tension, because these methods require visualobservation of the interface.

It is therefore a primary object of the present invention to provide anovel tensiometer assembly for use in combination with a substitutiontype analytical balance thereby extending use of the balance mechanismto measurement of the surface tension of a liquid interface.

It is also an object of the present invention to provide a noveltensiometer assembly that is of sufficient weight to approximate theweight of a balance pan that the tensiometer assembly replaces whenconverting a substitution type analytical balance to conductmeasurements of surface tension.

It is an even further object of the present invention to provide a noveltensiometer assembly the weight of which may be varied selectively toprovide a mechanism that may be substituted universally for the weighingpan devices of substitution balance instruments of various manufacture.

Among the several objects of the present invention is noted thecontemplation of a novel tensiometer assembly that may be adjustablyextended or shortened to compensate for differences in the height of theweighing chambers of substitution balances of different manufacture.

It is also an object of the present invention to provide a noveltensiometer assembly that includes means for controllably moving aliquid interface downwardly past a duNouy ring type tensiometermeasuring device.

Another object of the present invention contemplates the provision of anovel tensiometer assembly having the capability of utilizing themeasuring accuracy of a delicate substitution type analytical balancefor accurate determination of surface and interfacial tension of variousliquids including gas liquid interfaces and interfaces between quiescentliquids.

Another important object of the present invention concerns the provisionof a novel tensiometer assembly that allows efficient measurement ofinterfacial tension even though the liquid being measured might beopaque or murky preventing visual observance of the relative positionsof the interface and the duNouy ring.

'It is an even further object of the present invention to provide anovel tensiometer assembly that is simple in nature, low in cost andreliable in use.

Other and further objects, advantages and features of the presentinvention will become apparent to one skilled in the art uponconsideration of the written specification, the attached claims and theannexed drawings. The form of the invention, which will now be describedin detail, illustrates the general principles of I the invention, but itis to be understood that this detailed description is not to be taken aslimiting the scope of the present invention.

SUMMARY OF THE INVENTION A preferred embodiment of the present inventionmay comprise an elongated tensiometer assembly having a weight portionat the upper extremity thereof with a support eyeextending above theweight portion to be received by a support hook at the extremity of thearm of a substitution type analytical balance. A support stem extendsdownwardly from the weight portion and may be provided with a chuck orother suitable connection device for supporting a conventional duNouyring that may be suspended with the ring portion thereof immersed in aliquid belowthe interface that is to be measured. A container in whichthe liquid is contained may rest upon a support base that is selectivelymovable upwardly or downwardly by a motor mechanism that may be apneumatic or hydraulic jack device capable of raising or lowering thecontainer at a particular rate of speed. Also, if desired,the mechanismfor raising and lowering the container may comprise a mechanicalapparatus such as a scissors-type platform jack or a jack mechanism thatis actuated by an electric motor.

The support stem portion of the tensiometer assembly may be adjustableif desired to compensate for differences in overall height of theweighing chamber of substitution balances of different manufacture.Also, if desirable, the tensiometer assembly may include means formodifying the weight of the weight portion in order to compensate fordifferences in weight of the various weighing pans with whichsubstitution balances may be supplied.

The tensiometer assembly of this invention is also useful in themeasurement of the spreading velocity of surface active molecules. Toaccomplish measurement of surface molecule spreading velocity, anelongated narrow trough-like container is provided that is balanced upona support mechanism located outwardly of the weighing chamber of thebalance. A tensiometer assembly is suspended from the weighing arm ofthe analytical balance with a duNouy ring, carried thereby,

. 4 placed in the interface at an end of the trough disposed within theweighing chamber of the balance. The level of the trough is adjusted sothat the stationary distended interface is near the point of rupture.With the ring interface region in this condition the optical scalereading of the analytical balance is extremely sensitive to minutechanges in the interfacial tension. The experimenter than may add aknown quantity of surface active material or surfactant to the interfaceat the opposite end of the trough which are transmitted to the oppositeend of the trough at the spreading velocity of the surface activemolecules. Arrival of the first few molecules at the duNouy ring will beaccompanied by an immediate change of the optical scale reading of thesubstitution balance thereby giving a time-of-flight value of thesurface active molecules. The distance between the point of introductionof surfactant and the ring may then be divided by the time-of-flightvalue to yield the spreading velocity of the surface active molecules.

BRIEF DESCRIPTION OF THE DRAWINGS may be had by reference to theembodiments thereof which are illustrated in the appended drawings,which drawings form a part of this specification.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of the invention and are therefore not to beconsidered limiting of its scope for the invention may admit to otherequally effective embodiments.

In the drawings:

FIG. 1 is a pictorial representation of a substitution type analyticalbalance with the weighing pan thereof removed and a tensiometer assemblyconstructed in accordance with the present invention substituted for theweighing pan.

FIG. 2 is an elevational view of a tensiometer assembly of FIG. 1supporting a duNouy ring within a container of liquid supported by apneumatic motor shown partially in section.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2.

FIG. 4 is a fragmentary elevational view of a tensiometer assemblyrepresenting a modified embodiment of the present invention.

FIG. 5 is an elevational view of a container of liquid having a duNouyring supported therein, which container is adjusted manually by amechanical jack mechanism.

FIG. 6 is a fragmentary side elevational view of a substitution typeanalytical balance supporting a tensiometer assembly constructed inaccordance with the present invention and also showing a hydraulicallyenergized movable support mechanism supporting an elongated troughthereby adapting the tensiometer assembly for measurement of thevelocity of surface-active molecules.

DESCRIPTION OF PREFERRED EMBODIMENT Now referring to the drawings andfirst to FIG. 1, there is illustrated a substitution type analyticalbalance 10 having the usual digital readout mechanism 11 and adjustmentdials 12. A weighing arm 13 of the analytical balance extends from anenclosed housing 14 into a weighing chamber or compartment 15 andincludes at the free extremity thereof a support hook 16 that ordinarilyis utilized as a support for a weighing pan disposed within the weighingchamber 15. Except for removal of the weighing pan the substitution typeanalytical balance otherwise remains unaltered and retains itsconventional weighing capability.

To adapt a substitution type analytical balance for surface tensionmeasurements a tensiometer assembly may be substituted for the weighingpan of a balance. The tensiometer assembly of this invention mayconveniently take the form illustrated in FIG. 2 where there isdisclosed a tensiometer assembly illustrated generally at 17 including aweight portion 18 having a support tab 19 formed at the upper extremitythereof and presenting a support eye 20 to be received by the supporthook portion 16 of the weighing arm 13 of an analytical balance. Asupport stem 21 extends downwardly from the weight portion 18 which stemmay, if desired, be knurled to facilitate manipulation of a needle chuckmechanism 22 carried at the lower extremity of the support stem.Although the weight portion is illustrated as being disposed at theupper extremity of the support stem, it is not intended that thisparticular arrangement be limiting, it being obvious that the weightportion may be disposed at the intermediate portion or lower portion ofthe support stem, if desired. The needle chuck assembly 22 includes agripping portion 23 that is adapted to receive the support wire 24 of aconventional duNouy ring, illustrated generally at 25. It is notintended that the invention be limited to the use of a duNouy ringhowever, it being obvious that other devices such as a Wilhelmy Platemay also be supported by the tensiometer assembly and may be employed topreturb an interface. For purposes of simplicity however, the inventionwill be described in its relation with a duNouy ring type surfacetensiometer.

The duNouy ring includes a horizontal beam 26 having vertical supportelements 27 and 28 connected to the extremities thereof and supporting aring 29 that may be introduced below the surface or interface 30 of aliquid 31 contained within a measuring vessel 32. As shown in the lowerportion of FIG. 2, the measuring vessel 32 is supported by a supportbase 33 that may be moved upwardly or downwardly by a fluid motormechanism illustrated generally at 34.

The fluid motor mechanism incorporates a piston 35 disposed for movementwithin a cylinder 36 by a pressure fluid such as air introduced into achamber 37 below the piston by a hand pump assembly 38, which may be aflexible compressible bulb controlled by internal check valves inconventional manner and connected to the cylinder by a supply conduit39. The piston 35 may be secured to base 33 by an actuating stem 40. Abase 41 may be provided to support the fluid motor mechanism 34 and alsoto provide support for a bleed assembly 42 having a needle valve 43 thatmay be manually manipulated to control the exhaust of air from thechamber 37 through an exhaust conduit 44.

Alternative to the use of a pneumatic system for raising and loweringthe measuring vessel 32 to achieve the interface testing procedure asillustrated in FIG. 1, an electric motor 45 may be employed to achieverotation and thus reciprocation of a jack screw 46 connected to a base47 supporting the measuring vessel 32. Raising or lowering of the base47 may be achieved accurately through manipulation of the controls of aremote control mechanism 48 connected by a control cable 49 to theelectric motor 45.

In order to provide a universal tensiometer assembly that may beutilized with equal effectiveness with substitution balances ofdifferent manufacture, it may be necessary to vary the length of thetensiometer assembly to compensate for weighing chambers of differentheights and to vary the weigh of the tensiometer mechanism to compensatefor differences in weights of the weighing pans. A universal tensiometerassembly therefore may conveniently take the form illustrated in FIG. 4,where a tensiometer assembly illustrated at 50 may include a weightportion 51 that is suspended by a support eye in the same manner asdescribed above in relation to the tensiometer assembly 17 of FIG. 2.

The weight portion 51 of the tensiometer assembly may be provided withan annular flange 52 at the lower extremity thereof that may be formedintegrally with the weight portion 51 or may be secured to thetensiometer assembly 50 in any desirable manner. The annular flange 52presents an upper shoulder 53 that may be engaged to provide support fora plurality for weight rings or washers 54 that serve to effectivelyvary the weight of the tensiometer assembly thereby compensating fordifferences in weight of the balance pans for which the tensiometerassembly is to be substituted.

As illustrated in FIG. 5 a support stem 21a may be provided having aflange 52a adapted to support a weight 51a that when added to the weightof the support stem substantially equals the weight of a balance pan.The total weight of the tensiometer assembly may be adjusted simply byreplacing the removable weight 51a with another weight or by addingweight rings that may be received by the upper portion of the supportstem 21a as shown in broken lines at 540.

The tensiometer assembly 50 may also be provided with a support stemportion that can be elongated or shortened in order to compensate fordifferences in the height of the weighing chamber of analytical balancesof different manufacture. To achieve adjustable elongation or shorteningof the support stem portion of the tensiometer assembly, a support stemmay be composed of an upper stem section 55 of generally tubular form,within which is telescopically received a lower stem section 56. Theouter stem section 55 may be provided with a lower externally threadedextremity 57 having a plurality of fingers 58 defined by a plurality ofslots cut in the threaded portion of the upper support stem section. Alocking member 59, having internal threads 60, may be received by thethreaded portion 57 of the upper stem section 55 and may be manuallymanipulated to achieve sufficient movement of the fingers 50 to lock thetelescoping stem sections 55 and 56 in any suitable telescopingrelationship.

The lower stem section 56 may be provided with a needle chuck 61,constructed essentially identical with respect to the needle chuck 22,illustrated in FIG. 2. With a conventional duNouy tensiometer ringreceived within the needle chuck 61, the locking mechanism 50 may bemanipulated to unlock the telescoping relation between stem sections 55and 56 and the length of the tensiometer assembly 50 may be extended orshortened to position the duNouy ring in proper relationship withrespect to the interface of the liquid to be tested.

In the event the tensiometer assembly is found to be considerablylighter or heavier than the weighing pan nism for raising or loweringthe vessel 32 may conveniently take the form illustrated in FIG. 5,where a support base 62 of a mechanical jack mechanism may be employedto support the testing vessel 32. The jack mechanism may also employ abase 63 that may rest on the lower surface of the weighing chamber of ananalytical balance. A conventional scissors type jack mechanism,illustrated generally at 64, may be connected to the support plate 62and to the base 63 and may be manipulated by rotation of a shaft 64awhich through a conventional system of levers transmits rotary movementof the shaft 64a, through a threaded stem and bushing arrangement, intovertical movement of support plate 62. If the liquid 31 within container32 is of sufficient clarity to allow observation of the relativeposition of the ring portion 29 of the DuNouy ring, the relativepositions of the ring 29 and the interface 30 may be adjusted rapidly byrotating shaft 64a to place the interface 30 in close proximity to thering 29. Rotation of the shaft 64a then may be slowed to achieve anacceptably slow rate of downward movement in order to move the interface30 downwardly very slowly past the ring 29. The tension necessary tomove the interface downwardly past the ring 29 will of course bereflected on the digital readout mechanism of the analytical balance.

Referring now to FIG. 6, there is illustrated a testing arrangement bywhich the tensiometer assembly of FIGS. 2 and 4 may be employed tomeasure the spreading velocity of surface active molecules of aparticular liquid. To accomplish the testing procedure for determiningthe velocity of surface active molecules an elongated trough-like vesselis provided that may be supported in a stabilized generally horizontalposition with liquid disposed therein. One extremity B, of thetroughlike vessel 65 may be positioned within the analytical balanceweighing chamber and a conventional deNouy ring 25, supported by atensiometer assembly 17, may be disposed with the ring portion 29thereof so positioned that the juncture between the interface I and thering portion 29 will be in the distended condition that occursimmediately prior to rupture of the interface. To achieve this conditionthe vertical position of the elongated vessel 65 may be adjusted by anysuitable jack mechanism so that the stationary distended interface isnear the point of rupture. With the ring interface region in thiscondition, the optical scale reading of the analytical balance will beextremely sensitive to minute changes in the interfacial tension of theliquid within the vessel. The experimenter may then add a known quantityof a surface active material, also known as surfactant, to the interfaceat the opposite end A of the trough-like vessel 65 which changes thesurface tension of the liquid within the vessel. The changed quality ofthe surface tension will be transmitted by the surface active moleculesfrom point A to the duNouy ring, disposed at point 3", at the spreadingspeed of the surface active molecules of the liquid. As soon as thefirst few molecules arrive at the duNouy ring, an immediate change willtake place in the amount of force necessary to maintain the interface ina distended position. This force change will be optically presented bythe digital readout mechanism 11 of the analytical balance 10. The timerequired for the surface active molecules to traverse from point A tothe duNouy ring is a time-of-flight value of the surface activemolecules. The distance between the point of introduction of surfactantand the ring 29 may then be divided by the time-of-flight value to yieldthe spreading velocity of the surface active molecules.

The elongated trough-like vessel 65 may be supported by a hydraulic jackmechanism having a hydraulic cylinder 66 affixed to a support base 67that may rest on any suitable support outside of the weighing chamber 15of the analytical balance. The hydraulic cylinder 66 may include areciprocatable actuating stem 68 having a support plate 69 secured tothe upper extremity thereof and providing a support for the elongatedtrough-like vessel 65.

A hand pump 70 may be employed to supply pressurized hydraulic fluidfrom a reservoir R through a supply conduit 70a to the cylinder 66 belowthe actuating piston of the cylinder 66 for raising the piston upwardlyand thereby causing upward movement of the support plate 69. For thepurpose of lowering the support plate 69 for adjustment of the vessel65, a bleed valve mechanism 71 may be employed that is controlled by anadjustable needle valve 72 to bleed hydraulic fluid from the cylinder 66to the reservoir R" through a bleed conduit 73. The hydraulic jackmechanism is capable of infinite adjustment and provides an extremelystable platform upon which the trough-like container may rest. Theneedle valve 72 may be manipulated manually in order to bleed fluid fromthe cylinder 66 at a controlled rate thereby achieving controlleddownward movement of the measuring vessel and causing controlledrelative movement between the interface and the ring portion of theduNouy ring supported by the tensiometer assembly. The hydraulic jackmechanism illustrated in FIG. 5 is not intended for use only with theapparatus for measuring the speed of surface active molecules, it beingobvious that it may be employed in substitution for the electricallydriven jack structure set forth in FIG. 1, the pneumatic jack structureset forth in FIG. 2, or the manually adjustable mechanical jackstructure, illustrated in FIG. 5.

In view of the foregoing, it is evident that I have provided a noveltensiometer assembly that may be readily substituted for the weighingpan of substitution type analytical balances thereby converting theanalytical balance for measurement of the surface or interfacial tensionof a liquid medium. The tensiometer assembly may be properly weighted inorder to compensate for the weight of the weighing pan with which ananalytical balance may be provided. The tensiometer assembly mayincorporate means for varying the weight thereof to compensate for theweight of weighing pans of various balance manufacturers. Thetensiometer assembly may also be universally constructed for extensionto any suitable length in order to compensate for differences in heightof the weighing chambers of substitution type analytical balances ofdifferent manufacture.

A conventional duNouy ring may be supported by the tensiometer assemblyin substantially rigid relation to the tensiometer assembly by a needlechuck thereby enhancing the capability of a tensiometer assembly foraccurate measurement. By employing the tensiometer assembly of thisinvention and by substituting the same for the balance pan of asubstitution type analytical balance there is developed a measuringmechanism having the measuring accuracy of a delicate substitution typeanalytical balance for accurate determination of surface and interfacialtension of various liquids including gas liquid interfaces andinterfaces between quiescent liquids. The instant invention effectivelyallows the efficient measurement of interfacial tension even though theliquid being measured might be opaque or murky preventing visualobservance of the relative positions of the interface and the duNouyring. It is therefore seen that this invention is one well adapted toattain all of the objects and advantages hereinabove set forth, togetherwith other advantages which will become obvious and inherent from adescription of the apparatus itself. It will be understood that certaincombinations and subcombinations are of utility and may be employedwithout reference to other features and subcombinations. This iscontemplated by and is within the scope of the present invention.

As many possibleembodiments may be made of this invention withoutdeparting from the spirit or scope thereof, it is to be understood thatall matters hereinabove set forth, or shown in the accompanyingdrawings, are to be interpreted as illustrative and not in a limitingsense.

Having thus described my invention in detail, I claim:

1. In combination with a substitution type analytical balance having asupport arm with a support hook at the extremity thereof, theimprovement comprising:

a tensiometer assembly being of substantially the same weight as theweight of a weighing pan ordinarily supported by the support arm of saidbalance and having a support eye adapted to receive the support hook ofsaid support arm;

said tensiometer assembly depending directly from said support arm andhaving a needle chuck at the unsupported extremity thereof, said needlechuck receiving the vertical connector of said tensiometer ring andsupporting-said tensiometer ring in substantially rigid relation to saidtensiometer assemmeans containing a liquid substance having an interfacewith a fluid;

said tensiometer ring being supported with the ring portion thereofbelow said interface; and

means for controllably moving said interface relative to saidtensiometer ring.

2. The combination of claim 1 wherein:

said means for moving said interface away from said ring supportcomprises collapsible support means for said container; and

means for manually manipulating said collapsible support means tocontrol collapsing thereof and thereby to control downward movement ofsaid interface.

3. The combination of claim 1 wherein:

said means for moving said interface away from said ring supportcomprises a support base for said container means; and

motor means moving said support means and said container means at acontrolled rate thereby mov- 6 mg said tensiometer rmg through saidinterface at a controlled rate. 4. The combination of claim 1 wherein:

said means for moving said interface away from said ring supportcomprises a support base for said container means; and

fluid chamber means supporting said support base and having controllablebleed means for bleeding fluid from said fluid chamber means therebylowering said container means and moving said interface downwardlythrough said tensiometer ring at a controlled rate.

5. A tensiometer assembly for substitution type analytical balanceshaving a support arm defining a support hook, said tensiometer assemblycomprising:

support means having a support eye defined at the upper extremitythereof and receiving the support hook to suspend said tensiometerassembly from said support arm;

said support means being of substantially the same weight as theweighing pan assembly of an analytical balance;

a needle chuck being defined at the lower extremity of said supportmeans;

a vessel in which liquid may be placed to define an interface;

a tensiometer ring having a vertical support element being releasablyretained by said needle chuck assembly and supporting said tensiometerring in substantially rigid relation with said connector means with thering portion of said tensiometer ring disposed in generally horizontalmanner and being submerged in said liquid; and

means for moving said interface relative to said tensiometer ring toconduct measurement of interfacial tension of said liquid.

6. A tensiometer assembly as recited in claim 5:

means for selectively varying the weight of said tensiometer assembly.

7. A tensiometer assembly as recited in claim 5:

means for changing the overall length of said tensiometer assembly.

8. A tensiometer assembly as recited in claim 5:

said tensiometer assembly having an elongated stem being defined byupper and lower telescopically related stem sections; and

collet means releasably securing said stem sections in any desirabletelescoped position for varying the overall length of said tensiometerassembly.

9. A tensiometer assembly as recited in claim 5:

a support shoulder being defined on said tensiometer assembly; and

at least one removable weight means being supported by said supportshoulder for varying the weight of said tensiometer assembly.

10. A tensiometer assembly as recited in claim 5:

said means for moving said interface relative to said tensiometer ringcomprising a reciprocatable support for supporting said vessel; and

means for controlling vertical movement of said reciprocatable support.

11. A tensiometer assembly as recited in claim 5:

said means for moving said interface relative to said tensiometer ringcomprising a support plate upon which said vessel rests;

linear fluid motor means for imparting reciprocal movement to saidsupport plate; and

said fluid motor means having bleed means for accu rately establishing adesirable rate of downward movement of said interface relative to saidtensiometer ring.

Patent No. 3,780,569 Dated Decmbr 25, 19-13 Inventor (5;) John GrahamIt: is certified that error appclars in the above-identified patent andthat said Letters Patent are hereby corrected shown below:

Col 6, line 54; "50" should read 58"; C01. 6, line 60, "50" should read--59--.

Signed and sealed this 9th day of July 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer 7 Cqmmissionerof Patents

1. In combination with a substitution type analytical balance having asupport arm with a support hook at the extremity thereof, theimprovement comprising: a tensiometer assembly being of substantiallythe same weight as the weight of a weighing pan ordinarily supported bythe support arm of said balance and having a support eye adapted toreceive the support hook of said support arm; said tensiometer assemblydepending directly from said support arm and having a needle chuck atthe unsupported extremity thereof, said needle chuck receiving thevertical connector of said tensiometer ring and supporting saidtensiometer ring in substantially rigid relation to said tensiometerassembly; means containing a liquid substance having an interface with afluid; said tensiometer ring being supported with the ring portionthereof below said interface; and means for controllably moving saidinterface relative to said tensiometer ring.
 2. The combination of claim1 wherein: said means for moving said interface away froM said ringsupport comprises collapsible support means for said container; andmeans for manually manipulating said collapsible support means tocontrol collapsing thereof and thereby to control downward movement ofsaid interface.
 3. The combination of claim 1 wherein: said means formoving said interface away from said ring support comprises a supportbase for said container means; and motor means moving said support meansand said container means at a controlled rate thereby moving saidtensiometer ring through said interface at a controlled rate.
 4. Thecombination of claim 1 wherein: said means for moving said interfaceaway from said ring support comprises a support base for said containermeans; and fluid chamber means supporting said support base and havingcontrollable bleed means for bleeding fluid from said fluid chambermeans thereby lowering said container means and moving said interfacedownwardly through said tensiometer ring at a controlled rate.
 5. Atensiometer assembly for substitution type analytical balances having asupport arm defining a support hook, said tensiometer assemblycomprising: support means having a support eye defined at the upperextremity thereof and receiving the support hook to suspend saidtensiometer assembly from said support arm; said support means being ofsubstantially the same weight as the weighing pan assembly of ananalytical balance; a needle chuck being defined at the lower extremityof said support means; a vessel in which liquid may be placed to definean interface; a tensiometer ring having a vertical support element beingreleasably retained by said needle chuck assembly and supporting saidtensiometer ring in substantially rigid relation with said connectormeans with the ring portion of said tensiometer ring disposed ingenerally horizontal manner and being submerged in said liquid; andmeans for moving said interface relative to said tensiometer ring toconduct measurement of interfacial tension of said liquid.
 6. Atensiometer assembly as recited in claim 5: means for selectivelyvarying the weight of said tensiometer assembly.
 7. A tensiometerassembly as recited in claim 5: means for changing the overall length ofsaid tensiometer assembly.
 8. A tensiometer assembly as recited in claim5: said tensiometer assembly having an elongated stem being defined byupper and lower telescopically related stem sections; and collet meansreleasably securing said stem sections in any desirable telescopedposition for varying the overall length of said tensiometer assembly. 9.A tensiometer assembly as recited in claim 5: a support shoulder beingdefined on said tensiometer assembly; and at least one removable weightmeans being supported by said support shoulder for varying the weight ofsaid tensiometer assembly.
 10. A tensiometer assembly as recited inclaim 5: said means for moving said interface relative to saidtensiometer ring comprising a reciprocatable support for supporting saidvessel; and means for controlling vertical movement of saidreciprocatable support.
 11. A tensiometer assembly as recited in claim5: said means for moving said interface relative to said tensiometerring comprising a support plate upon which said vessel rests; linearfluid motor means for imparting reciprocal movement to said supportplate; and said fluid motor means having bleed means for accuratelyestablishing a desirable rate of downward movement of said interfacerelative to said tensiometer ring.